Cathodic electrodeposition of highly porous cobalt sulfide counter electrodes for dye-sensitized solar cells

In this study, cobalt sulfide (CoS) counter electrodes (CEs) fabricated by potentiodynamic deposition in a near-neutral solution (pH 6) were incorporated into Pt-free dye-sensitized solar cells (DSSCs). It was found that the potentiodynamic deposition mode can facilitate the formation of CoS within the deposit compared to the conventional chronoamperometric deposition. Different sweep cycle (charge capacity) had great impact on the morphology and electrocatalytic activity of CoS films. The CoS film fabricated by five-sweep-cycle potentiodynamic deposition was observed with highly porous morphology and multilayer structure, thus resulting in a lower charge-transfer resistance of similar to 1.03 Omega cm(2) in comparison with a sputtered-Pt CE. The DSSC assembled with this kind of CoS CE showed a higher photovoltaic conversion efficiency of 6.33+/-0.15% compared to 6.06+/-0.17% for DSSC with the sputtered-Pt CE under full sunlight illumination (100 mW cm(-2), AM 1.5G). In addition, consecutive cyclic voltammetric and long-term light soaking tests demonstrated that such DSSC had excellent stability. Therefore, the highly porous CoS film can be considered as a promising alternative CE for use in DSSC due to its high electrocatalytic performance and electrochemical stability. (C) 2011 Elsevier Ltd. All rights reserved.